全文获取类型
收费全文 | 2852篇 |
免费 | 185篇 |
国内免费 | 646篇 |
专业分类
测绘学 | 114篇 |
大气科学 | 218篇 |
地球物理 | 1273篇 |
地质学 | 1225篇 |
海洋学 | 388篇 |
天文学 | 128篇 |
综合类 | 93篇 |
自然地理 | 244篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 40篇 |
2020年 | 27篇 |
2019年 | 34篇 |
2018年 | 49篇 |
2017年 | 12篇 |
2016年 | 39篇 |
2015年 | 52篇 |
2014年 | 60篇 |
2013年 | 72篇 |
2012年 | 140篇 |
2011年 | 217篇 |
2010年 | 63篇 |
2009年 | 80篇 |
2008年 | 176篇 |
2007年 | 180篇 |
2006年 | 175篇 |
2005年 | 169篇 |
2004年 | 166篇 |
2003年 | 122篇 |
2002年 | 118篇 |
2001年 | 104篇 |
2000年 | 133篇 |
1999年 | 62篇 |
1998年 | 68篇 |
1997年 | 64篇 |
1996年 | 77篇 |
1995年 | 79篇 |
1994年 | 86篇 |
1993年 | 108篇 |
1992年 | 112篇 |
1991年 | 112篇 |
1990年 | 99篇 |
1989年 | 80篇 |
1988年 | 89篇 |
1987年 | 60篇 |
1986年 | 43篇 |
1985年 | 44篇 |
1984年 | 42篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 35篇 |
1979年 | 6篇 |
1973年 | 6篇 |
1964年 | 6篇 |
1959年 | 7篇 |
1958年 | 15篇 |
1957年 | 9篇 |
排序方式: 共有3683条查询结果,搜索用时 15 毫秒
1.
Bimal Raj SHRESTHA Binu TIMSINA Zuzana MüNZBERGOVá Tomás DOSTáLEK Prakash GAUDEL Tej B.BASNET Maan B.ROKAYA 《山地科学学报》2020,17(5):1115-1127
Butterflies are widely studied due to their key ecosystem functions.For this reason,they are used in ecosystem assessment,formulating conservation plans and in raising the environmental awareness.Quantification of different factors affecting diversity of butterflies is important for their effective conservation.In this study,we investigated abiotic and biotic factors affecting species richness and community composition of butterflies along an elevational gradient in Manang region,central Nepal.We also tested if butterfly species follow the Bergmann’s rule.A total of 57 butterfly species belonging to 39 genera and 8 families were recorded in the study area.Out of a total of 127 plant species identified in the study region,only 67 plant species were visited by butterflies as nectar sources.Species richness of butterflies increased with increasing elevation.Species richness was significantly higher in places with shrubs compared to other places and also in autumn than in summer.Species richness of butterflies also depended on composition of plant species occurring at the localities.Butterfly species composition varied among sampling localities.It was also determined by habitat type,elevation,sampling time,plant species and interactions of elevation×time.The relationship between butterfly size and elevation was in the opposite direction than expected according to the Bergmann’s rule.In conclusion,protection of butterfly diversity can only be achieved by protecting different habitats across the diverse physiography of the region and different plant species,in particular herbs and shrubs.Our results do not support the Bergmann’s rule for butterflies along an elevational gradient in our region. 相似文献
2.
The effect of river runoff over the northern Indian Ocean(NIO) especially over the Bay of Bengal(Bo B) has been studied using global Nucleus for European Modelling of the Ocean(NEMO). Two sensitivity experiments, with and without river runoff are conducted and the influence of river runoff on the Indian Ocean hydrography,stratification and circulation features are studied. It is found that due to river runoff surface salinity over the northern Bo B decreases by more than 5 and the East India Coastal Current strengthens by 2 cm/s during post monsoon season. The fresh river water reaches up to 15°N in the Bo B and is the main cause for low salinity there.Sea surface temperature in the northwestern Bo B increases by more than 0.2℃ due to the river runoff in summer monsoon while surface cooling upto 0.2℃ is seen in north-west part of Bo B in winter season. The seasonal mixed layer depth in the region is found to be dependent on river runoff. The effect of vertical shear and Brunt Vaisala frequency on stratification is also examined. The ocean water becomes highly stratified up to 3 035 m due to the river runoff. It is found that the energy required for mixing is high in the northern and coastal Bo B. 相似文献
3.
4.
5.
6.
7.
8.
9.
Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel–peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightly contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their ~(87) Sr/~(86) Sr and ~(143) Nd/~(144) Nd isotopic compositions in addition to their classifications based on their chemical compositions(alkaline and calc-alkaline). These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone. 相似文献
10.
Osama M. KASSEM Yousef A. ALAMRI Faisal K. ZAIDI Abdel Aziz M. AL BASSAM Mansour H. AL-HASHIM 《《地质学报》英文版》2021,95(3):750-760
The vorticity analysis technique was applied to measure the different lithological units,such as schist,metagranite and metavolcano-sedimentary rocks,which are present in the Halaban region.This work aims to interpret the relationship between the different lithologies and the tectonic setting,in order to elucidate the nature of kinematic analysis in the Halaban region.The kinematic analyses were applied to feldspar porphyroclasts,quartz and hornblende for twentysix samples.The kinematic vorticity number (W_m) for deformed rocks in the study area ranged from~0.6 to 0.9.The direction of the long axes for finite strain data (X axes) revealed a WNW trend with shallow dipping.The direction of the short axes for finite strain data (Z axes) were represented by vertical with associated horizontal foliation.The results of the kinematic vorticity and strain analyses are characterized by simple shear with different degrees of deformation in the Halaban region.Furthermore,our finite strain data shows no significant volume change during deformation.The subhorizontal foliation was synchronized with thrusting and deformation.Furthermore,throughout the overlying nappes,the same attitudes of tectonic contacts are observable,the nappes in the orogens being formed from simple shear deformation. 相似文献